During fabrication, a semiconductor device undergoes a variety of processing steps such as physical vapor deposition, chemical vapor deposition, etching and the like. Many of these processes, particularly etching, are performed within corrosive processing chamber environments (e.g., NF.sub.3, F, and/or O.sub.3 at elevated temperatures). These corrosive environments may attack and corrode the various parts within the processing chamber, such as heaters, electrical coils, chamber walls, clamp rings, collimators, shields, etc. Therefore, processing chamber parts must be resistant to corrosive processing environments, so as not to degrade and possibly contaminate a semiconductor device being processed within the chamber.
Further, a number of corrosive fabrication processes involve the deposition of material layers on a semiconductor substrate. As material is deposited on a semiconductor substrate, it also deposits on processing chamber parts, and in turn may flake therefrom, contaminating semiconductor substrates processed therewithin. To prevent such contamination, chamber parts are periodically etched to remove deposited material. Thus, many processing chamber parts must be resistant to the deposited material's etchant, such that selective etching may occur.
Accordingly, when constructing a part for use within a semiconductor processing chamber, the selection of materials that exhibit not only favorable surface characteristics (e.g., corrosion resistance, or desired etch properties), but also exhibit favorable bulk characteristics (e.g., inexpensive, easily manufactured, good thermal conductivity, desirable magnetic properties, strength, etc.) presents a significant challenge. To broaden the universe of materials that may be used for processing chamber parts, coated parts are often employed wherein an underlying part is formed of a material that exhibits desired bulk characteristics, and a material that exhibits desired surface characteristics is applied thereto. While such coated parts somewhat ease the material selection process, coated parts can present a significant source of contamination when processing at elevated temperatures. Specifically, as the processing chamber thermally cycles (e.g., between various processing, cleaning or maintenance steps) so do the processing chamber's coated parts. If an underlying part and its coating differ in thermal coefficient of expansion, during thermal cycling the underlying part and the coating will expand and contract at different rates, resulting in stress therebetween (i.e., thermal stress). Such thermal stress can cause the coating material to flake from the underlying part, leaving the underlying part exposed to corrosive processing gases, and, moreover, introducing potential contaminants to the processing atmosphere. Thus, because of the need to match thermal coefficients of expansion, the practice of coating parts introduces additional constraints to the material selection process.
A need therefore exists for processing chamber parts which satisfy both the bulk characteristics and the surface characteristics required for a given processing environment, without introducing undesirable particles thereto.